This invention pertains to apparatus for aligning and calibrating two cooperating diagnostic X-ray systems.
In angiographic examinations, it is frequently necessary to obtain X-ray views of a blood vessel in two different directions simultaneously. For example, posterior-anterior (PA) and lateral X-ray views of the same vessel may be required. Apparatus for acquiring PA views of a blood vessel or any part of the anatomy is shown in U.S. Pat. No. 4,339,825. The apparatus shown in that patent is frequently referred to as a frontal imaging system (FIS).
Apparatus for obtaining lateral views is available from various X-ray equipment manufacturers. One such apparatus is described in U.S. Pat. application Ser. No. 421,603, filed Sept. 22, 1982, now U.S. Pat. No. 4,501,011, which is incorporated herein by reference. The referenced application is assigned to the assignee of this application. The referenced application discloses a so-called vascular gantry system (VGS) that includes an X-ray source and an X-ray image receptor that are angulatable synchronously with each other and capable of being aligned transversely to the frontal imaging system. The vascular gantry system is used for obtaining a lateral X-ray view simultaneously with obtaining a PA or frontal X-ray view.
A problem in obtaining simultaneous PA and lateral X-ray views is assuring that the central ray in the X-ray beam projected from the X-ray source to the image receptor in the frontal imaging system will continue to intersect the central ray of the lateral viewing system at a common point, called the isocenter, for all angular orientations of both systems. Accurate alignment of the vascular gantry system is difficult because it is comprised of two separate mechanisms that may be uncoupled from each other. Since all vascular examination procedures do not require lateral X-ray views, it is desirable to have a vascular gantry- system that can be easily separated from and restored to the vicinity of the patient undergoing examination in a frontal imaging system. However, when the two systems are brought into cooperating relation, it is important that alignment of the systems is assured without requiring any effort or thought by the system operator or technician.
As indicated, the two systems are aligned when their isocenters are coincident and remain coincident at all angles. The isocenter is more specifically defined as a point on the central X-ray of an X-ray beam extending from the focal spot of the X-ray tube to the center of an X-ray image receptor, such as an image intensifier, which point is intercepted by the horizontal and vertical axes about which the tube and receptor orbit or angulate jointly about the patient being examined. The patient is desirably supported in a position such that the common isocenter of both of the two systems lies on the plane in the patient containing the organ or blood vessel that is the subject of lateral and frontal X-ray views. If the isocenters do not coincide, the X-ray image produced by one system will be shifted spatialy relative to the other. In other words, each system will view a slightly different part of the region of interest in the anatomy. It is important that the isocenters of the two systems remain coincident for any angulation of the two pairs of X-ray sources and image receptors.